padata: do not leak refcount in reorder_work

In the Linux kernel, the following vulnerability has been resolved:

padata: do not leak refcount in reorder_work

A recent patch that addressed a UAF introduced a reference count leak:

the parallel_data refcount is incremented unconditionally, regardless

of the return value of queue_work(). If the work item is already queued,

the incremented refcount is never decremented.

Fix this by checking the return value of queue_work() and decrementing

the refcount when necessary.

Resolves:

Unreferenced object 0xffff9d9f421e3d80 (size 192):

comm "cryptomgr_probe", pid 157, jiffies 4294694003

hex dump (first 32 bytes):

80 8b cf 41 9f 9d ff ff b8 97 e0 89 ff ff ff ff ...A............

d0 97 e0 89 ff ff ff ff 19 00 00 00 1f 88 23 00 ..............#.

backtrace (crc 838fb36):

__kmalloc_cache_noprof+0x284/0x320

padata_alloc_pd+0x20/0x1e0

padata_alloc_shell+0x3b/0xa0

0xffffffffc040a54d

cryptomgr_probe+0x43/0xc0

kthread+0xf6/0x1f0

ret_from_fork+0x2f/0x50

ret_from_fork_asm+0x1a/0x30